1. Field of the Invention
The present invention relates to an image processing apparatus and a conversion method thereof for converting image data read by a scanner into a vector format.
2. Description of Related Art
It has recently become common to scan paper documents using a scanner and store the scanned documents in digitized form. The documents thus scanned by the scanner are stored, for example, as image data in bitmap format.
The bitmap format expresses characters as a group of dots (pixels), and thus it is not necessary to perform complex calculations when displaying or printing those characters. However, the bitmap format has a disadvantage in that “jaggies” (aliasing artifacts) may be noticeably visible in the contours of the characters displayed or printed depending on the resolution of the apparatus (output apparatus) that outputs (displays or prints) the characters.
A process called “outlining” has therefore been conventionally performed so as to convert bitmap images into vector font images (vector images).
In a vector image, a character is reproduced by forming contour lines by approximating the contours of the character to straight lines and curved lines and then filling in the regions surrounded by those contour lines, which renders jaggies less apparent. Furthermore, because the outputted result does not depend on the resolution of the output apparatus, the image quality of character portions can be stabilized easily even if the output apparatus changes. However, it is necessary to increase the number of points (contour points) used to reproduce the contours of a character in order to express the character as accurately and smoothly as possible in a vector image. As a result, maintaining the image quality of character portions significantly increases the amount of data.
An image processing apparatus has been proposed as conventional technology regarding vector images (JP-2007-129557-A).
According to the image processing apparatus in JP-2007-129557-A, image data obtained by scanning a document is divided according to attributes such as character size, font, color, and outlining is performed according to each piece of data into which the image data is divided.
However, as described above, there are situations where converting the image to a vector image increases the overall amount of image data. The number of contour points increases particularly with characters that have complex shapes, and thus the increase in the data amount is especially prominent in cases where such characters are numerous. Although reducing the number of contour points can be considered in such a case, doing so risks altering the shape of the character, and thus such a method is not favorable.